Controlled feeding of powdered material

ABSTRACT

A method of controlled feeding of powdered material, for example, an explosive powder, comprises feeding a material through the outlet of a mass flow hopper, feeding gas under pressure to the material above the hopper outlet, and adjusting the gas pressure to maintain the flow of powdered material at a predetermined value. The invention also includes an apparatus for feeding the powdered material and a method and apparatus for manufacturing explosive fuse-cord wherein the explosive material is fed by the aforesaid method.

United States Patent Turner Mar. 12, 1974 [5 CONTROLLED FEEDING 0F POWDERED 757,580 4/1904 Truyter et a1. 86/22 ux MATERIAL 1,517,878 12/1924 Wasmayr..... 3,004,462 10/1961 Cook et a1. 86/1 R [75] Inventor: Trevor John Turner, Ardrossan,

Scotland Primary Examiner--Leland A. Sebastian [73] Assignee: Imperial Chemical Industries Attorney, 8 Firmcushmanr Darby &

Limited, London, England Cushman 22 d: 19, l 72 1 me 9 57 ABSTRACT [21 1 Appl' 264404 A method of controlled feeding of powdered material, for example, an explosive powder, comprises feeding a [52] U.S. C1. 86/1 R, 57/8, 86/22, m ri l r gh the outlet of a mass flow pp 93/78, 250/435 FC feeding gas under pressure to the material above the [51] Int. Cl C06b 21/02 pp Outlet and adjusting the g Pressure to main- [58] Field of Search 57/8; 86/1 R, 22; 93/78; tain the flow of powdered material at a predetermined 250/435 FC value. The invention also includes an apparatus for feeding the powdered material and a method and ap- [5 6] References Cited paratus for manufacturing explosive fuse-cord wherein UNITED STATES PATENTS 7/1857 Andrews 57/8 the explosive material is fed by the aforesaid method.

10 Claims, 1 Drawing Figure CONTROLLED FEEDING OF POWDERED MATERIAL This invention relates to a method and apparatus for controlled feeding of powdered material. The method is especially advantageous for feeding sensitive explosive powder. The invention also includes a method of manufacturing fuse-cord wherein the material for the core of the fuse-cord is fed by the said method and apparatus.

In many manufacturing processes an accurately controlled feed of powdered material is required. Freerunning powders are generally metered by means of a screw feed mechanism or by gravitational flow through an orifice. The former is unsuitable for feeding sensitive explosive powders, as required, for example in explosive fuse-cord manufacture and for this purpose the latter method has been traditionally used. This method, however, is not always sufficiently accurate and variation in the charge per unit length of cord results, especially between different batches of explosive core material.

It is an object of this invention to provide an improved method and apparatus for feeding powdered material whereby sensitive explosive powders can be more uniformly fed in fuse-cord manufacture. A further object is to improve the method of manufacture of explosive fuse-cord.

In accordance with this invention a method of controlled feeding of a powdered material comprises feeding the material under gravitational mass flow conditions through the outlet of a mass flow hopper for the said material, feeding gas under pressure to the material above the hopper outlet, and adjusting the gas pressure by means responsive to the rate of flow of powdered material through the hopper outlet to maintain the rate of flow of powdered material at a predetermined value.

A mass flow hopper is a hopper wherein, when the outlet is open, the whole contents are in motion and there is no stationary material as occurs in core flow hoppers. The method of designing a mass flow hopper for a given material has been described by Jenike in Bulletin No. 123, University of Utah Engineering Experiment Station.

From a further aspect the invention includes an apparatus for feeding powdered material comprising a mass flow hopper for the said material, the said hopper having a perforate wall portion adjacent to its outlet, means to feed gas under pressure through the said perforate wall portion to the interior of the hopper, means for monitoring the flow of powdered material from the outlet of the hopper and gas pressure control means,

responsive to the rate of flow of powdered material, arranged to vary the pressure ofgas being fed through the said perforate wall portion of the hopper so as to maintain the flow of powdered material at a predetermined value. v

The perforate wall portion of the hopper may be a portion of the hopper having one or more holes therethrough but preferably it is fabricated from porous material such as sintered metal, and it is further preferred that the perforations should be sufficiently small in order to prevent the powder to be fed to the apparatus inadvertently passing through the perforate wall portion. To facilitate feeding gas into the hopper, the perforate wall portion is conveniently surrounded by a jacket or manifold connected to gas supply means. The means for monitoring the flow of powdered material is conveniently a beta-ray monitor and the gas pressure control means conveniently comprises an electropneumatic converter which varies the gas pressure in accordance with an electric signal from the monitor.

The invention further includes a method of manufacturing explosive fuse-cord wherein powdered explosive material is fed through a mass flow hopper in a controlled manner by the aforesaid method of the invention to form the core of a fuse-cord and the core is wrapped with protective wrapping materials.

Also included in the invention is apparatus for the manufacture of explosive fuse-cord, which apparatus comprises the aforesaid apparatus of the invention for feeding powdered material and means to wrap protective wrapping materials around a stream of powdered explosive material after the emergence of the powdered material from the mass-flow hopper. In a preferred apparatus the wrapping means comprises means to fold a tape into a tubular envelope around the stream of powder and means to wind one or more reinforcing layers of spun textile yarn around the said tubular envelop thereby forming what is generally termed a semifuse. The apparatus preferably also includes extrusion means for applying an outer water-proofing layer of synthetic plastics material to the semi-fuse.

The invention is hereinafter further described, by way of example, with reference to the accompanying drawing which shows diagrammatically in sectional elevation an apparatus in use for the manufacture of a fuse-cord.

The apparatus includes a tapered mass flow hopper 10 for explosive material 11 having a perforate wall portion 12 above its outlet 13. The hopper is surrounded by ajacket 14 into which an air supply may be delivered through an inlet tube 15. A tapered guide tube 16 surrounds the jacket 14 and is positioned to leave an annular space around the jacket 14 into and through which space a tape 17 can be fed and curved along its longitudinal axis under the influence of the guide tube 16 to form a tubular envelope around material emerging from the hopper outlet 13. A die 18 below the outlet is so shaped and positioned to receive the tubular envelop and consolidate the explosive contents thereof without restricting the flow of material from the hopper outlet 13.

Two horizontal axially spaced counter rotatable platforms 19 and 20 having central hubs 21, 22 and central apertures 23, 24 are positioned below the die 18 and co-axial therewith. Each platform is adapted to carry a plurality of freely rotatable textile bobbins 25 from which textile yarns 26 may be drawn and applied in continuous helical manner to the outside of the continuously descending tubular envelope to form the semifuse. A press die 33 positioned between the platforms l9 and 20 is adapted further to consolidate and crush the explosive powder core. An extruder 27 is adapted to extrude an outer layer of synthetic thermoplastic material 28 around the textile wrappings to form finished fuse. Although for convenience the extruder is illustrated with the apparatus for making the semi-fuse, in general, the extrusion of the thermoplastic sheath is a separate manufacturing stage.

A beta-ray emitter and monitor 29 disposed between the platforms l9 and 20 is adapted to measure continuously the amount of powdered explosive material 11 in the core of the fuse-cord. The monitor 29 is electrically connected to an electro-pneurnatic converter 30 which controls the amount of compressed air from an air supply 31 which is fed to the tube 15.

In operation a centre thread 32 is continuously drawn through the hopper 10, die 18, aperture 23, die 33, and aperture 24. A paper tape is drawn through the annular space inside the guide tube 16 in which it is curved into tubular form, and is then drawn through dies 18 and 33 and apertures 23 and 24. The hopper is filled with explosive powder 11, for example, pentaerythritol tetranitrate, and air is fed around the powder through inlet tube 15. The powder 11 emerging from the hopper is received in the tubular envelope formed from tape 17 and is consolidated by its passage through die 18 to form the core of the fuse-cord and further consolidated and crushed in die 33. The textile layers are continuously applied to the outside of the continuously descending tubular envelope, a first spun layer being applied from the yarns on bobbins 25 on platform 19 and a second counterspun layer being applied from the bobbins on platform 20. The core loading is monitored by the betaray monitor 29 and the pressure of the air supplied through inlet tube is appropriately adjusted to maintain the flow of powder 11 at the desired rate.

The cross sectional area of the hopper outlet is conveniently chosen so that the approximate loading is delivered without any air supply and the degree of perforation of the perforate wall portion 12 is conveniently chosen so that small air pressure variations have a marked effect on the material flow. A small initial air pressure results in a very steep increase in the flow rate but after the initial increase further increase in the air pressure results in a gradual diminution of flow and it is more practical to adjust the apparatus so that the required material flow is in this latter region.

EXAMPLE In this example PETN powder was fed through a mass flow hopper 10 having a perforate wall portion 12 adjacent to the outlet through which wall portion air was fed under pressure around the PETN in the aforedescribed manner.

The PETN had the following sieve analysis:

Passing BSS 14 mesh 100 percent Passing BSS 36 mesh 90% Passing B53 52 mesh 77% Passing B55 72 mesh 29% Passing B88 100 mesh 6% The flow through the hopper outlet varied with the air pressure in the jacket 14 surrounding the perforate wall portion in the following manner:

Using a beta-ray monitor to monitor the powder flow in connection with an electro-pneumatic converter to control the air pressure, the flow of powder could be controlled to within i 5% of the desired value at least over the range 76 to 200 grams/minute.

What I claim is:

1. A method of controlled feeding of powdered material, which comprises feeding a stream of the material under gravitational mass flow conditions through the outlet of a mass flow hopper for said material, feeding gas under pressure around the outside of the stream of material immediately above the hopper outlet and adjusting the gas pressure by means responsive to the rate of flow of powdered material through the hopper outlet to maintain the rate of flow of powdered material at a predetermined value.

2. An apparatus for feeding powdered material by the method of claim 1, comprising a mass flow hopper for the said material, the said hopper having a perforate wall portion adjacent to its outlet, means to feed gas under pressure through the said perforate wall portion to the interior of the hopper, means for monitoring the flow of powdered material from the outlet of the hopper and gas pressure control means, responsive to the rate of flow of powdered material, arranged to vary the pressure of gas being fed through the said perforate wall portion of the hopper so as to maintain the flow of powdered material at a predetermined value.

3. An apparatus as claimed in claim 2 wherein the perforate wall portion is fabricated from porous material.

4. An apparatus as claimed in claim 3 wherein the porous material comprises sintered metal.

5. An apparatus as claimed in claim 2 wherein the perforate wall portion of the hopper is surrounded by a jacket or manifold connected to gas supply means.

6. An apparatus as claimed in claim 2 wherein the means for monitoring the flow of powdered material comprises a beta-ray monitor.

7. An apparatus as claimed in claim 2 wherein the gas pressure control means comprises an electropneumatic converter which varies the gas pressure in accordance with an electric signal from the monitor.

8. A method of manufacturing explosive fuse-cord wherein powdered explosive material is fed through a mass flow hopper by a method in accordance with claim 1, to form the core of a fuse-cord and the core is wrapped with protective wrapping materials.

9. An apparatus for the manufacture of explosive fuse-cord, the apparatus comprising apparatus as claimed in claim 2 together with means to wrap protective wrapping materials around a stream of powdered explosive material after the emergence of the powdered material from the mass flow hopper.

10. An apparatus as claimed in claim 9 wherein the wrapping means comprises means to fold a tape into a tubular envelope around the stream of powder and means to wind one or more reinforcing layers of spun textile yarn around the said tubular envelope.

. UNITED STATES. PATENT OFFICE CERTIFICATE OF CORRECTION 7 Patent No. 3 r 796 r 126 Dated March 12 1974 Inventor) Trevor John Turner It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Please insert the following in the heading:

Foreign Application Priority Data June 25, l97l v Great Britain 29907/71 Signed and sealed this 17th day of September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR; c. MARSHALL DANN Attesting Officer Commissioner of Patents FORM Po-1o50 (10-69) 'uscoMM-oc seam-pea UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 317961126 Dated March 12 1974 Inventor) Trevor John Turner It: is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Please insert the following in the heading:

Foreign Application Priority Data June 25, 1971 7 Great Britain 29907/71 Signed and sealed this 17th day of September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. 7 C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM F G-1050 (10-69) USCOMM-DC bean-pea 

1. A method of controlled feeding of powdered material, which comprises feeding a stream of the material under gravitational mass flow conditions through the outlet of a mass flow hopper for said material, feeding gas under pressure around the outside of the stream of material immediately above the hopper outlet and adjusting the gas pressure by means responsive to the rate of flow of powdered material through the hopper outlet to maintain the rate of flow of powdered material at a predetermined value.
 2. An apparatus for feeding powdered material by the method of claim 1, comprising a mass flow hopper for the said material, the said hopper having a perforate wall portion adjacent to its outlet, means to feed gas under pressure through the said perforate wall portion to the interior of the hopper, means for monitoring the flow of powdered material from the outlet of the hopper and gas pressure control means, responsive to the rate of flow of powdered material, arranged to vary the pressure of gas being fed through the said perforate walL portion of the hopper so as to maintain the flow of powdered material at a predetermined value.
 3. An apparatus as claimed in claim 2 wherein the perforate wall portion is fabricated from porous material.
 4. An apparatus as claimed in claim 3 wherein the porous material comprises sintered metal.
 5. An apparatus as claimed in claim 2 wherein the perforate wall portion of the hopper is surrounded by a jacket or manifold connected to gas supply means.
 6. An apparatus as claimed in claim 2 wherein the means for monitoring the flow of powdered material comprises a beta-ray monitor.
 7. An apparatus as claimed in claim 2 wherein the gas pressure control means comprises an electro-pneumatic converter which varies the gas pressure in accordance with an electric signal from the monitor.
 8. A method of manufacturing explosive fuse-cord wherein powdered explosive material is fed through a mass flow hopper by a method in accordance with claim 1, to form the core of a fuse-cord and the core is wrapped with protective wrapping materials.
 9. An apparatus for the manufacture of explosive fuse-cord, the apparatus comprising apparatus as claimed in claim 2 together with means to wrap protective wrapping materials around a stream of powdered explosive material after the emergence of the powdered material from the mass flow hopper.
 10. An apparatus as claimed in claim 9 wherein the wrapping means comprises means to fold a tape into a tubular envelope around the stream of powder and means to wind one or more reinforcing layers of spun textile yarn around the said tubular envelope. 